1. Field of the Invention
The present invention relates to a charged particle beam apparatus enabling a user to observe the micro-sample extracted from, for example, a semiconductor device substrate while performing micro-machining and a sample fabrication method using the charged particle beam apparatus.
2. Description of the Related Art
The technique of micro-machining using a focused ion beam (FIB) is disclosed, for example, in WO099/05506. By applying an FIB to a sample, it is possible to perform micro-machining using the sputtering phenomenon. Accordingly, it is possible to extract a micro-sample, for example, from a semiconductor device substrate. Moreover, by introducing a deposition gas into the vicinity of the FIB irradiation of the sample and performing the FIB irradiation in the gas atmosphere, a deposition film is formed by the ion beam assisted deposition phenomenon. This film formation can be used for a type of micro-bonding. By installing a probe for lifting out a micro-sample in an FIB sample chamber having a deposition gas supply source, it is possible to fix a micro-sample extracted by the FIB machining to the probe by the FIB deposition film formation, separate it from the sample substrate, and lift out it. The lifted out micro-sample can be fixed to a micro-sample holding unit pre-arranged in the vicinity of the sample substrate in the same sample chamber. The micro-sample holding unit has a shape facilitating its mounting on a sample holder of a transmission electron microscope (TEM) or a scanning transmission electron microscope (STEM) from the viewpoint of operability.
The technique concerning the combination of the FIB apparatus and the STEM is disclosed in JP-A-2004-228076 and JP-A-2002-29874. JP-A-2004-228076 shows that the sample for observation by using the STEM fabricated by the FIB machining is placed at the intersection of the ion beam axis and the electron beam axis and can be additionally machined by the FIB and observed by the STEM. The thin film surface of the STEM sample should be placed almost parallel for additional machining by the FIB and almost vertically for the observation by the STEM. However, according to this technique, the ion beam axis intersects the electron beam axis at an acute angle (about 45 degrees in FIG. 5) and the STEM sample should be rotated around the rotation axis vertical to the both axes between the FIB additional machining and the STEM observation. Moreover, JP-A-2002-29874 also shows an example of intersection of the ion beam axis and the electron beam axis at an acute angle (about 50 degrees in FIG. 1).
On the other hand, JP-A-6-231720 discloses a technique concerning fabrication of a TEM sample. In this technique, in order to check the film thickness of the TEM sample to be thin-film-machined by the FIB, an electron beam is applied in vertical direction with respect to the cross section of the sample so as to detect an intensity ratio between the electron beam irradiation intensity and the electron beam which has transmitted through the sample. Here, the transmitted electron beam does not distinguish detection of a transmitted beam having a very small scattering angle as an STEM signal from the scattered beam which has transmitted and scattered and the sample film thickness is not monitored from the STEM observation point. The similar technique is also disclosed in JP-8-5528. Moreover, JP-A-6-231719 discloses an apparatus characterized in that a FIB irradiation system is arranged in the vertical direction with respect to the TEM electron beam axis in the sample chamber of the TEM apparatus and the TEM sample fabricated by the FIB machining can be directly observed by the TEM without extracting the TEM sample into the atmosphere, thereby solving the problem of a low throughput during the FIB additional machining. JP-A-6-231719 also discloses a TEM image monitor as control of the sample film thickness.
Moreover, JP-A-7-92062 discloses an example of the in-situ TEM observation of a sample being subjected to FIB machining. However, since the FIB is introduced not vertical to the sample surface, there is a defect that a beam damage is made deeper as compared to the cross section thin film sample which is fabricated almost parallel to the FIB incident axis.
As for the STEM single apparatus, it is disclosed, for example, in JP-A-2000-21346. The beam scan image detecting a transmitted electron from the sample for use as a brightness signal is called a bright field image while the beam scan image detecting a scattered electron for use as a brightness signal is called a dark field image. The contrast of the bright field image reflects absorption, diffraction, and phase shift of the irradiated electron in the sample. On the other hand, the dark field image uses only the diffracted electron, which is reflected in a particular angle direction, for use as a brightness signal and the size of the crystal grain is clearly appears. The bright field image and the dark field image are both images (STEM images) formed by the beam which has transmitted through the sample and very helpful for analysis of the thin film structure.
Moreover, the irradiated electron beam of the STEM apparatus conventionally has a high energy in the order of 200 keV like the TEM. However, recently, the STEM observation is performed in the energy region of 30 keV like the conventional SEM as reported in Journal Electron Microscopy 51(1):53-57(2002). When the electron beam irradiation energy is lowered, the transmission capability of the thin film sample is also lowered. Accordingly, in the low-energy STEM apparatus, a highly accurate film thickness management is normally required for the thin film sample fabricated by the FIB machining.